Orbital sander

ABSTRACT

AN ORBITAL SANDER WHEREIN THE OUTPUT SHAFT OF A MOTOR CARRIES AN ECCENTRIC INTERMEDIATE SHAFT CONNECTED WITH A DISK-SHAPED COUNTERWEIGHT WHICH ROTATES IN A COMPARTMENT DEFINED BY TWO SECTIONS OF THE SANDING PAD. EACH SECTION OF THE PAD IS PROVIDED WITH AN ANTIFRICTION BEARING FOR THE INTERMEDIATE SHAFT. THE PAD IS ARTICULARLY CONNECTED WITH THE HOUSING OF THE SANDER BY SEVERAL ELASTIC PINS WHICH EXTEND INTO REGISTERING RECESSES TAPERING IN DIRECTIONS AWAY FROM EACH OTHER AND RESPECTIVELY PROVIDED IN THE UPPER SECTION OF THE PAD AND IN A CLOSURE FOR THE MOTOR.

Oct. 5, 1971 A. SCHNIZLER ETA!- 3,609,922

' ORBITAL SANDER Filed Feb. 17. 1969 Fig.1 2

a as H 1 9 Fig. 2 IV Fi 4 34 g 41 INVENTOR 44/4/2501 r Smmueq Hen/1 ,11km? BY W I 6f f-n r 'zr ATTORNEY United States Patent O 3,609,922ORBITAL SANDER Albrecht Schnizler, Nurtingen, and Hermann Kieser,Oberensingen, Germany, assignors to Metabowerke KG. Closs, Ranch &Schnizler, Nurtingen, Wurttemberg, Germany Filed Feb. 17, 1969, Ser. No.799,792 Claims priority, application Germany, Feb. 20, 1968, P 16 52131.6 Int. Cl. B24!) 7/00, 23/02 US. Cl. 51-170 T 24 Claims ABSTRACT OFTHE DISCLOSURE BACKGROUND OF THE INVENTION The present invention relatesto power tools in general, and more particularly to improvements inportable orbital sanders, also known as pad sanders.

It is already known to assemble the sanding pad of an orbital sander oftwo sections including a lower or outer section which is surrounded bysandpaper and an inner or upper section which is mounted for axialmovement on an eccentric motion-transmitting shaft by means of a needlebearing accommodated in a cup of the upper section. The output shaft ofthe motor which drives the motion transmitting shaft is formed with acollar which partially surrounds the cup and carries severalcounterweights. The coupling means for articulately connecting the padto the housing of the sander comprises an elastic ring which is securedto selected portions of the housing and to selected portions of the pad.A drawback of such sanders is that the useful life of the elastic ringis very short and that the assembly of balancing weights consumes muchtime. Also, such sanders comprise an excessive number of parts.

SUMMARY OF THE INVENTION An object of our invention is to provide anorbital sander or pad sander wherein the sanding pad and thecounterweight are constructed and mounted in a novel way and wherein thecouping means between the pad and the housing of the sander undergoesless wear than in presently known sanders.

Another object of the invention is to provide an orbital sander which isconstructed in such a way that the hand of the operator is subjected tonegligible shaking forces when the sander is in use and which comprisesa relatively small number of simple parts.

A further object of the invention is to provide an orbital sander whichcan be assembled or taken apart with little loss in time, which canemploy a relatively small and light counterweight, and wherein suchcounterweight need not be assembled of two or more parts.

Still another object of the invention is to provide novel and improvedbearings for that part in an orbital sander which imparts orbitalmovements to the pad.

The improved orbital sander comprises a housing, an electric motor orother suitable prime mover secured to the housing and having a compositeor one-piece output ice member including a first portion rotatable abouta first axis and a second portion having a second axis which is parallelto the first axis, a sanding pad including two interconnected sectionsdefining between themselves a compartment for a preferably disk-shapedcounterweight which is non-rotatably mounted on the second portion ofthe output member, and a pair of antifriction bearings for the secondportion of the output member; these bearings flank the counterweight andeach thereof is provided or mounted in one section of the sanding pad.The coupling means for articularly connecting the sanding pad to thehousing comprises rod-shaped bolts or pins each of which extends into atapering recess of the housing and into a registering tapering recess inthat section of the pad which is located between the counterweight andthe prime mover. The counterweight is preferably provided with aneccentric hub which is mounted on the second portion of the outputmember between the two bearings and has a fiat abutting against acomplementary flat on the second portion of the output member.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved orbital sander itself, however, both as to its construction andits mode of operation, together with additional features and advantagesthereof, will be best understood upon perusal of the following detaileddescription of certain specific embodiments with reference to theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a fragmentary partlyelevational and partly longitudinal sectional view of an orbital sanderwhich embodies our invention;

FIG. 2 is a plan view of the counterweight;

FIG. 3 is a fragmentary horizontal sectional view as seen in thedirection of arrows from the line III-III of FIG. 1; and

FIG. 4 is a sectional view as seen in the direction of arrows from theline IV-IV of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1,there is shown a portion of an orbital sander or pad sander whichcomprises a sanding pad 1 orbitable in response to rotation of theoutput shaft 3 of a prime mover 2, preferably an electric motor. Themeans for imparting orbital motion to the sanding pad 1 comprises anintermediate shaft 4 parts of which are eccentric with reference to theoutput shaft 3. The shafts 3, 4 constitute first and second portions ofa composite output member. The shaft 3 is rotatably mounted in a radialantifriction bearing 32 which is installed in an extension or lowerportion 5 of a housing 6. The latter supports the motor 2 and isprovided with a trigger 7 which is depressible to complete the motorcircuit. The output shaft 3 has a conical part 8 which is received in acomplementary socket of the intermediate shaft 4. The latter is furtherformed with internal threads meshing with the externally threaded tip 9of the output shaft 3. If desired the shafts 3 and 4 can form anintegral onepiece output member.

The sanding pad 1 comprises two sections including a plate-like lowersection 11 (hereinafter called plate for short) and a cupped uppersection 10 (hereinafter called cover). Antifriction bearings 13 and 12for the intermediate shaft 4 are respectively mounted in the plate 11and cover 10. The bearing 13 in the plate 11' is lighter than thebearing 12 in the cover 10. The inner races of the bearings 12, 13respectively surround eccentric median and lower end portions 14, 15 ofthe intermediate shaft 4. The cover 10 has a hub which is formed with acylindrical'recess 16 for the outer race of the bearing 12.

This outer race is held against axial movement toward the output shaft 3by a split ring 18. The lower end face of the outer race of the bearing12 abuts against an internal annular shoulder 17 of the cover 10. Theplate 11 comprises a panel '20 of rubber which is immediately adjacentto the smooth side of a sheet of sandpaper (not shown) and is overlappedby a liner 19 of sheet metal. The central portion of the liner 19 isformed with an opening for a bearing sleeve 21 which is recessed intothe elastic panel 20 and has an annular flange which overlies theadjoining portion of the liner 19. The sleeve 21' accommodates the outerrace of the antifriction bearing 13. The mounting of the bearing 13 ispreferably such that the centers of spherical rolling elements 22 arelocated in or close to the plane of the liner 19.

In accordance with a feature of our invention, the counterweight 23 ismounted in a compartment 24 at the underside of the cover 10. Thecounterweight 23 comprises a circular disk '25 (see FIG. 2) whose axisis shown at 26. The disk 25 has a hub 27 which is spaced from the axis26 and is non-rotatably mounted on the median portion 14 of theintermediate shaft 4. To this end, the median portion 14 is preferablyprovided with at least one fiat 29 and the through bore of the hub 28 issurrounded by an internal surface having a complementary flat 29a andsnugly receiving the median portion 14 to thus insure that thecounterweight 23 shares all angular movements of the intermediate shaft4. If desired, the hub 27 can be mounted on a specially machined secondmedian portion of the intermediate shaft 4 between the median portion 14and the end portion 15. The axis of the hub 27 coincides with the axis28 of the output shaft 3. The centers of gravity of the counterweight 23and sanding pad 1 are preferably located on a line which is parallelwith the axis 28. This insures that the shaft 3 is not subjected to anyappreciable bending stresses and that the sander does not shake the handof the operator when the motor 2 is on. The numeral 30 denotes in FIG. 2the eccentricity of the counterweight 23; the extent of sucheccentricity is preferably substantial because there is enough room inthe compartment 24 to permit rotary movement of the counterweight withthe intermediate shaft 4. This is of advantage because the weight of thedisk 25' can be reduced proportionally with increasing eccentricity. Aperfect balance is achieved if the weight of the disk 25 plus the weightof the hub 27 multiplied by eccentricity 30 equals the weight of thesanding pad 1 multiplied by the much smaller eccentricity 31 of theportions 14, 15 (bearings 1'2, 13) with reference to the axis 28 of theoutput shaft 3.

During assembly of the sander, the cover 10 is installed in a firststep, followed by the counterweight 23 and thereupon by the plate 11.The latter is then secured to the cover 10 by screws, bolts or analogousfasteners, not shown. The outer race 33 of the antifriction bearing 32for the output shaft 3 is mounted in a closure 34 which forms part of oris secured to the aforementioned extension 5 of the housing 6. The innerrace 35 of the bearing 32 is mounted on the upper part 36 of theintermediate shaft 4; this upper part 36 is coaxial with the outputshaft 3.

The coupling means for articulately connecting the pad 1 to the housing6 and for limiting the extent of angular displacement of the pad withreference to the closure 34 of the extension 5 comprises pins or bolts39 which consist of rubber or other suitable elastomeric material. Thesebolts 39 extend into recesses or bores 37, 38 respectively provided inthe lower end face of the closure 34 and in the upper end face of thecover 10. The elasticity of bolts 39 is such that they permit orbit-a1movements of the pad 1 to the extent determined by eccentricity 31 ofthe bearings 12, 13 with reference to the axis 28 of the output shaft 3.The recesses 37, 3'8 taper inwardly, namely, away from the respectiveend faces, and each thereof is surrounded by a frustoconical internalsurface of the closure '34 or cover 10. The conicity is selected in sucha way that it corresponds to the inclination of the correspondingportion of the respective bolt 39 when the sander is in use. Each bolt39 preferably resembles a solid circular cylinder (see FIG. 3) and itsexternal surface abuts against the surfaces surrounding the respectiverecesses 37, 38 to thereby reduce friction to a minimum. The bolts 39are subjected only to compressive stresses. The aforementioned end facesof the cover 10 and closure 34 are prefer-ably immediately or closelyadjacent to each other (see FIG. 4) to thus limit the free dom ofmovement of bolts 39. In order to reduce or eliminate bending stresseson the bolts 39, the closure 34 is preferably provided with projectionsor noses 41 which extend into complementary depressions or recesses ofthe cover 10. The latter is formed with projections or noses 40 whichextend with minimal freedom into corresponding depressions or recessesof the closure 34. If the output member including the shafts 3 and 4 isrotated in the direction indicated by arrow 42 (FIG. 3), the projection40 pushes the adjoining bolt 39 against the corresponding projection 41to thus prevent excessive angular displacement of the pad 1 counter tothe direction indicated by arrow 42. The closure 34 of the extension 5is further provided with stops 43 which serve as abutments for theprojections 40 of the cover 10 (see FIG. 4). In order to avoid excessiveimpacts, each stop 43 can be provided with a cushion (not shown) ofrubber or the like. The bolts 39 are held against rotation in theirrecesses 37, 38 by keys or protuberances 44 which are provided in therecess 37 and/ or 38 and extend into grooves or recesses 45 provided inthe peripheral surfaces of the bolts. External stresses which arise whenthe sander is in use tend to rotate the bolts counter to the directionof rotation of output shaft 3.

An important advantage of the improved sander is that the hand of theoperator holding the housing 6 is subjected to negligible shaking forcesor to no shaking forces at all. This is due to novel mounting of thecounterweight 23 and pad 1 which insures that the output shaft 3 is notsubjected to any bending stresses. Another important advantage of thesander is that it can be used for extended peri ods of time withoutnecessitating replacement of any parts excepting the sandpaper which ismounted on the pad 1 in the customary way, for example, by means oflever action fasteners or the like, not shown. The bolts 39, namely,such parts which correspond to parts most likely to wear away and torequire frequent replacement in conventional orbital sanders, can standlong periods of use because they are subjected to negligible bendingstresses and wear. Furthermore, the bolts 39 insure very satisfactoryguidance of the pad 1. Still another advantage of the sander is that itcomprises a relatively small number of simple parts which can be readilyassembled and taken apart for periodic inspection and/ or cleaning. Thisapplies particularly for the machining of plate 11, cover 10,

counterweight 23 and intermediate shaft 4 as well as for the mounting ofbearings 12, 13 and 32. The overall length of the tool as seen in theaxial direction of the output shaft 3 is small so that the tool is handyand can be used for light as well as heavy-duty sanding.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying ccurrent knowledge,readily adapt it for various applications without omitting featureswhich fairly constitute essential characteristics of the generic andspecific aspects of our contribution to the art.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:

1. In an orbital sander, a combination comprising a housing; a primemover secured to said housing and having an output member including afirst portion rotatable about a first axis and a second portion defininga second axis which is parallel to said first axis; a pad including twointerconnected sections defining between themselves a compartment;coupling means articulately securing said pad to said housing; saidcoupling means comprising a plurality of elastic bolts, said housing andsaid pad being provided with registering recesses in which opposite endportions of said bolts are received; a counterweight accommodated insaid compartment and fixed to the second portion of said output member;and a pair of bearings for the second portion of said output member,said bearings flanking said counterweight and each thereof beingprovided in one of said sections to effect orbital movements of said padin response to rotation of said output member.

2. A combination as defined in claim 1, wherein one of said sections islocated between said counterweight and said prime mover and is providedwith a recess constituting said compartment.

3. A combination as defined in claim 1, wherein said counterweightcomprises a disk and a hub surrounding the second portion of said outputmember.

4. A combination as defined in claim 3, wherein said disk is a circulardisk and said hub is adjacent to the axis of said circular disk.

5. A combination as defined in claim 3, wherein said hub and the secondportion of said output member comprise abutting fiats which preventrotation of the output member with reference to said counterweight.

6. A combination as defined in claim 1, wherein the second portion ofsaid output member comprises a part which transmits torque to saidcounterweight and has an axis coinciding with said first axis.

7. A combination as defined in claim 1, wherein one section of said padis located between said counterweight and said prime mover and whereinthe other section of said pad comprises an elastic panel and a liner ofmetallic material overlying said panel adjacent to said compartment.

8. A combination as defined in claim 7, further comprising a sleevefixed to said liner and surrounding that bearing which is provided insaid other section.

9. A combination as defined in claim 7, wherein the bearing which isprovided in said other section comprises an annulus of rolling elementshaving centers located in the general plane of said liner.

10. A combination as defined in claim 7, wherein the bearing which isprovided in said other section is lighter than the bearing provided insaid one section.

11. A combination as defined in claim 1, wherein the second portion ofsaid output member is provided with a tapering socket receiving aconical part of said first portion.

12. A combination as defined in claim '1, wherein one portion of saidoutput member is provided with external threads and the other portion ofsaid output member is provided with internal threads mating with saidexternal threads.

13. A combination as defined in claim 1, further comprising a thirdbearing having an outer race mounted in said housing and an inner racesurrounding a part of the second portion of said output member, saidpart having an axis which coincides with said first axis.

14. A combination as defined in claim 13, wherein said housing comprisesa closure for said prime mover and wherein the outer race of said thirdbearing is mounted in said closure.

15. A combination as defined in claim 1, wherein the portions of saidoutput member are integral with each other.

16. A combination as defined in claim 1, wherein said housing comprisesa closure for said prime mover and one section of said pad is adjacentto said closure, said recesses being provided in said one section and insaid closure.

17. A combination as defined in claim 1, wherein one of each pair ofsaid recesses tapers in a direction away from the other recess.

18. A combination as defined in claim 17, wherein the taper of saidrecesses is a function of the distance between said axes.

19. A combination as defined in claim 1, further comprising means forpreventing rotation of said bolts in the respective recesses.

20. A combination as defined in claim 19, wherein said last mentionedmeans comprises protuberances provided in at least one of each pair ofregistering recesses and a groove provided for such protuberance in therespective bolt.

21. A combination as defined in claim 1, wherein said pad is provided'with first projections each adjacent to one of said bolts and eachextending into a recess provided therefor in said housing and whereinsaid housing is provided with second projections adjacent to said boltsand each extending into a recess provided therefor in said pad.

22. A combination as defined in claim 21, wherein each of said firstprojections is located substantially diametrically opposite one of saidsecond projections with reference to the axis of the respective bolt.

23. A combination as defined in claim 21, further comprising stopsprovided on said housing and each adjacent to one of said firstprojections.

24. A combination as defined in claim 1, wherein each of said bolts isof circular cross-sectional outline.

References Cited UNITED STATES PATENTS 3,375,616 4/1968 Scott 51l702,786,313 3/1957 Shafi 51-170 2,639,564 5/1953 Atkin 51-170 HAROLD D.WHITEHEAD, Primary Examiner

